RE: Ian/Jesper/Remi - Isonic 115 & Fins
While I'm not in a position to say what size would best suit the iSonic 115, I can say that Tectonic fins are excellent quality fins. I have Goldwings (34cm, 36cm & 38cm), a 46cm Spitfire and a 50cm Mirage. Given the sizing recommended by Jesper Orth above, the F8 Tomcat would be the line you should consider. Actually, it's the latest updated version of the older Spitfire line. However, if Spitfires are still available in your locale, it clearly remains a worthy choice.